<!DOCTYPE html>
<script>
var popups = 0;
window.addEventListener('message', function(a) {
  if (a.data == 1) {
    let popup = !!window.open();
    popups += popup ? 1 : 0;
  } else {
    window.domAutomationController.send(popups);
  }
});

// Tries to open two popups and reports how many successfully opened.
function openPopupsAndReport() {
  window.postMessage(1, document.location);
  window.postMessage(1, document.location);
  window.postMessage(2, document.location);
}
</script>
